The present invention relates generally to a plasma processing system.
Conventionally, in order to carry out a plasma processing, e.g., etching process, of an object to be processed, e.g., a semiconductor wafer (which will be hereinafter referred to as a "wafer"), is used a capacitive coupled etching system, i.e., a parallel plate etching system, wherein a substantially cylindrical susceptor serving as a lower electrode is provided at a lower portion of a processing chamber formed in a substantially cylindrical sealed processing container and wherein a substantially disk-shaped upper electrode is provided at a location facing the susceptor.
In such a capacitive coupled etching system, a wafer is first mounted on the susceptor, and then, a processing gas is introduced into the processing chamber maintained at reduced pressure. Thereafter, when a high-frequency power for producing plasma is applied to the upper electrode via a feeding rod, the processing gas introduced into the processing chamber dissociates to excited plasma. Then, ions in the plasma are effectively drawn into a surface to be processed, by a high-frequency bias power applied to the susceptor, so that a desired etching process is carried out.
An inductively coupled etching system is also used, which can carry out a process at a higher etching rate than that of the capacitive coupled etching system by enhancing the density of plasma in the processing chamber. In such an etching system, a substantially cylindrical susceptor serving as a lower electrode is arranged at a lower portion in a substantially cylindrical sealed processing container, and a substantially annular high-frequency coil is arranged on the outer periphery of the processing container via a dielectric wall.
When an etching process is carried out using the inductively coupled etching system, a wafer is first mounted on the susceptor, and then, a processing gas is introduced into a processing chamber maintained at reduced pressure. Thereafter, when a high-frequency power is applied to the high-frequency coil, an electric field is produced in the processing chamber via the dielectric wall. This electric field causes the processing gas in the processing chamber to dissociate to excited plasma. Then, ions in the plasma are effectively drawn into a surface of the wafer to be processed, by a high-frequency bias power applied to the susceptor, so that a desired etching process is carried out.
Recently, with the super high integration and miniaturization of semiconductor devices, more hyperfine patterning technology has been required. Also in etching processes, it has been required to further improve an etch selectivity and to develop a system which can process a larger wafer at a high etching rate, in order to improve the productivity.
Thus, in order to carry out the etching process of a wafer at a high etch selectivity and at a high etching rate, it has been attempted to enhance the density of plasma in a processing chamber and to change the position at which a processing gas is introduced.
However, in order to enhance the density of plasma in the capacitive coupled etching system, a high-output high-frequency power must be applied to the upper electrode, and a self-bias voltage produced by the high-frequency power is also increased with the output ascension of the high-frequency power. Consequently, during an etching process, the upper electrode is sputtered by the ions in the plasma so as to be significantly consumed, so that there is a problem in that the lowering of throughput may result from the required exchange of the upper electrode.
In addition, near the connecting portion of the feeding rod and the upper electrode in the capacitive coupled etching system, impedance is suddenly changed due to the difference between the lateral cross-sections thereof. Therefore, with the output ascension of the high-frequency power applied to the upper electrode, there are problems in that electric current may flow through the surface of an insulating material, which is provided so as to surround the upper electrode, to cause a dielectric electric breakdown or power damping, so that heat may be produced to damage the insulating material.
Moreover, the inductively coupled etching system can generate a high-density plasma in the processing chamber by increasing the output of a high-frequency power applied to a high-frequency antenna. However, there is a problem in that the inner wall surface of the processing container may be sputtered so as to be damaged. In addition, when the pressure in the processing chamber is relatively high, e.g. 20 mTorr or more, plasma may be biased so as to exist in the peripheral portion of the processing container, so that the density of plasma may be uneven so as to lower the stability and repeatability of the etching process.
In addition, in the inductively coupled etching system, a coil is wound onto the outer periphery of the processing container a plurality of times, so that the size of the processing container is increased. Also, when the size of the processing container is further increased as the diameter of the wafer is increased, it is difficult to obtain a desired reduced-pressure atmosphere. Consequently, the residence time of the gas in the processing chamber is increased, so that a reaction gas dissociates excessively to decrease the etch selectivity and to decrease the exhaust efficiency of a reaction product. Therefore, there is a problem in that the reaction product may be not only adhered to an object to be processed, to decrease the yield, but it may also be adhered to the inner surface of the processing container and the upper electrode.